It is known that liquid-liquid extractions can remove water from liquid organics, remove volatile organics from water, or separate an organic mixture. In chemical processes, liquid-liquid extractions are often used to transfer a solute dissolved in a first liquid to a second liquid. The second liquid may be partially miscible or essentially immiscible with the first liquid. The first liquid can generally be termed the "feed solution" and the second liquid is generally termed the "extractant." In an undissolved state, the solute can be a solid, liquid or gas. The solute tends to distribute itself between the two liquids in accordance with the relative solubility of the solute in the two liquids when the feed solution is brought into contact with the extractant.
In the past, most liquid membrane based processes were unstable due either to dissolution or evaporation into the surroundings. A number of separation devices have been described.
U.S. Pat. No. 3,956,112 to Lee, et al., May 1976, issued relates generally to an extraction process in which a porous membrane serves as a partition between two immiscible solvents. Solutes from one solvent are transferred to the other by way of the porous membrane via direct solvent-solvent contact. In practice, conventional extraction processes in which immiscible solvents are separated by a porous membrane generally do not prevent one solvent from forming a dispersion in the other. One or the other solvent typically seeps through the porous membrane and becomes dispersed in the solvent on the other side of the membrane. Consequently, conventional extraction processes involving immiscible solvents separated by a porous membrane often provide a settling tank and a solvent return mechanism to coalesce any dispersion formed by the seepage of one of the solvents through the membrane and to return the solvent so recovered to its source [B. M. Kim, Membrane based extraction for selective removal and recovery of metals, J. Membrane Sci., 21 (1984) 5-19].
U.S. Pat. No. 4,750,918 to Sirkar, issued June 1988, relates to an apparatus which permits a gas to be selectively transferred from a feed gas mixture to an output fluid.
U.S. Pat. No. 4,973,434 to Sirkar et al., issued November 1990, relates to a single-ply immobilized liquid membrane comprising an aqueous liquid membrane which is immobilized within a hydrophobic microporous support, and the process for making such a membrane.
U.S. Pat. No. 4,789,468 to Sirkar, issued December 1988, relates to an apparatus for liquid-liquid solute-transfer. The apparatus consists of a feed solution chamber, a liquid extractant chamber, and a pressure-difference regulator. In operation, the feed solution is pumped into the feed solution chamber at a substantially constant rate under pressure. The extractant is pumped into the extractant chamber at a controlled pressure. The feed solution contacts one side of a porous membrane, while the extractant contacts the other side of the porous membrane. One of the two phases, the feed solution or the extractant, wets the pores of the membrane. Pressures of the feed solution and the extractant are imposed, in directions and magnitude, to substantially immobilize the interface between the feed solution and the extractant at the porous membrane. The solute passes through the pores of the membrane into the extractant. The extractant is then discharged from the housing. This invention provides for removal of the solute from the extractant by using a second chamber where a phase similar to the feed phase is used. Thus the solute is not recovered as such.
U.S. Pat. No. 4,921,612 to Sirkar, issued May 1990, relates to an asymmetrically-wettable porous membrane and a process for transferring solute from a liquid feed solution to a liquid extractant, which is substantially immiscible with the feed solution. The housing of the unit has an asymmetrically-wettable porous membrane that divides the interior of the housing into a feed chamber, into which a feed solution is pumped then discharged, and an extractant chamber, into which an extractant is pumped then discharged. The side of the membrane facing the aqueous feed solution chamber is hydrophilic, whereas the side of the membrane facing the organic extractant chamber is hydrophobic. Pores in the membrane permit communication between the feed solution and the extractant. The solute diffuses into the extractant. The extractant containing the solute is then discharged from the unit.
U.S. Pat. No. 5,053,132 to Sirkar, issued October 1991, is a continuation of the previously discussed patent which relates to the asymmetrically-wettable porous membrane.
Notwithstanding the foregoing, the inventors herein have recognized that there is a need in the art for a separation device that does not require discharge of the extractant liquid.
The citation of any reference herein should not be deemed an admission that such reference is available as prior art to the invention.